1. Field of the Invention
The invention relates to a fan motor control method, and in particular to a fan motor control device.
2. Description of the Related Art
Electronic systems generate heat based on the amount of data they process. Because some electronic systems provide fast and continuous operations, heat dissipation devices for these electronic systems are more important. Various heat dissipation products are provided for users, and fan systems are currently popular among the most.
FIG. 1 depicts a conventional fan system. A fan system comprises a fan motor 1 and a control device 2 controlling the fan motor 1. The control device 2 is electrically connected to the fan motor 1 to control the fan motor 1.
The control device 2 comprises a clock signal generator 20, a digital-to-analog converter (DAC) 21, and a drive unit 22. The clock signal generator 20 generates a low-frequency clock signal S1. The low-frequency clock signal S1 can be a pulse width modulation (PWM) signal, and the frequency of the low-frequency clock signal S1 is less than 23 KHz. The DAC 21 is electrically connected to the clock signal generator 20 that receives the low-frequency clock signal S1 (digital signal) and converts into a voltage signal S2, which is an analog signal. The drive unit 22 is electrically connected to the DAC 21 and the fan motor 1 to receive the voltage signal S2. The voltage signal S2 is amplified and converted from digital to analog by the drive unit 22 to obtain a low-frequency drive signal S3. The low-frequency drive signal S3 is input to the fan motor 1 to drive the fan motor or adjust the rotation speed of the fan motor. It notes that the frequency of the low-frequency drive signal S3 output from the drive unit 22 is quite low, typically about 30 to 300 Hz. According to the following formulas, if an input frequency (f) is low, a ripple voltage (Vr(pp)) is high such that a ripple factor is high. This result in the rotation speed of the fan motor 1 is vibrated according to frequency response. Thus, the stability of the rotation rate is not satisfied and makes the noise and vibration if the rotation rate of the fan motor 1 is low.r=Vr(pp)/Vo;Vr(pp)=(1/fRLC)*Vop;
Moreover, the users cannot control the duty cycle of the fan motor 1 in a range of 0%-100% by controlling the fan motor 1 with the low-frequency drive signal S3. The rotation speed of the fan motor controlled by the users only in a range of 30%-80% at most. It limits controllable ration speed and thus is not satisfied by the demand of the users. Therefore, it is an important subjective to provide an improved fan system.